Luminous reflecting lamp



March 23, c D E v LUMINOUS REFLECTING LAMP Filed Aug. 7, 1936 Patented 1 93 LUMINDUS REFLECTING LAMP Clarence Birdseye, Gloucester, Mass., assignoi' to Birdseye Electric Corporation, Dover, DeL, a corporation of Delaware Application August'l,

8 Claims.

This invention relates to incandescent lamps which have a part of the bulb surface coated with an opaque reflecting medium, such as metallic silver, disposed in such a way that the light beam is directed in some controlled manner or pattern on the area to be illuminated. Generally the fllament in such lamps is hooded by the opaque reflecting surface, and practically all of the light from the incandescent source impinging on the 10 reflecting surface is reflected through the transmitting portion of the bulb to the area to be usefully illuminated. This obviously increases the efficiency of illumination on the desired area but it practically eliminates direct light from the lamp in behind or above the reflecting surface.

For many purposes such reflecting lamps placed in socket fixtures furnish a complete installation-no external reflector or housing being required. In other installations, such as in store illumination, it is desirable for artistic effect to enclose the lamp bulb, or several lamp bulbs, in a translucent enclosure or to associate them with other types of reflecting or light diffusing devices acting directly or indirectly to con- 5 trol the lighting effect.

When an ordinary non-reflecting bulb is associated with such a translucent or opalescent enclosure, since the light leaves the bulb at high intensity in all directions, the enclosure is illuminated approximately uniformly over its entire surface. When on the other hand, a reflecting bulb, as described above, is so used a part of the enclosure is definitely much darker than the rest, due to the fact that the reflecting surface of the bulb entirely prevents direct light from the incandescent source from striking this part of the enclosure. The shadowed part of the enclosure is, of course, dimly lighted by indirect reflections from the smooth inside of the translucent enclosure, but, compared with the brightly illuminated part of the enclosure, it is dim and unattractive. On the other hand, that part of the enclosure through which practically all of the light from the incandescent source is transmitted, comprising the direct light and the light reflected by the silvered surface, is more brilliant than is the case with an ordinary non-reflecting bulb of the same wattage in the same enclosure, and the result of this is at once apparent on the counters of astore, for example, over which such an installation is used. On the other hand despite the diffusing efiect of the opalescent enclosure, the reflecting bulb used in this way puts a greatly increased amount of the total light on to the counter and floor where it is useful, rather than 1936, Serial No. 94,760

wasting it in horizontal rays and high up on the ceiling. The increased efliciencyratio of useful light to total light emitted by incandescent source-is apparent and readily measureable.

In my endeavor to produce, for use in such a translucent enclosure, a reflecting bulb which would be not only highly efflcient as a light concentrator but also one which would produce a desirable appearance of the .enclosure itself, it became evident that the dark shadowed portion of the enclosure-shaded by the reflecting surface of the bulb-must be rendered somewhat brighter, so that the contrast between the two parts of the enclosure would be less marked and preferably unnoticed. It is desirable that this be accomplished without disturbing to any great extent the high efficiency obtained by the reflecting bulb on the store counters, for example, and other parts of the room usefully illuminated. Whatever light is subtracted from that otherwise employed to illuminate the useful zone, is largely wasted, so, but little must be used for the purpose of removing the shadow from the dark area of the enclosure.

There are certain other requirements that should be met inaccomplishing the desired results. Any light thrown on the darker part of the enclosure must be uniformly distributed, and in any case there must be no light patterns bright or dark spots; and if possible, the apparent brilliance of the shadowed portion should approach that of the brilliantly illuminated transmitting portion of the enclosure.

In my endeavor to reach a satisfactory solution of this difficult and important problem, I attempted to use an expedient that is old in the art-I removed a band, or concentric bands, from the silver coating so that direct light from the incandescent source would pass through and illuminate the enclosure. These bands varied in width from about inch to inch. This proved entirely unsatisfactory. Not only was such a large part of the reflecting surface removed that a noticeable reduction in lighting efficiency on the useful area occurred, but each band cast a brilliant ring of light onto theenclosure, and these rings were separated by alternate rings of shadow. Moreover, when the rings were A; to inch in width, and when used, for example, in an overhead direct translucent enclosure fairly close to the ceiling, these alternate rings of light and shadow were transferred to the ceiling.

I have made the important discovery that the shadowed portion of the enclosure may be brightly illuminatedso that no objectionable contrast 2 aovaaae exists between it and the brilliantly illuminated transmitting portion of the enclosure--and, so that this shadowed portion is uniformly illuminated without rings or other alternate areas of light and shadow, and therefore without rings or other designs on the ceiling, for example, by removing a very small part of the total reflecting surface in a series of flne marks or apertures distributed over the reflecting surface, and by doing this in connection with a frosted or etched area on the surface of the incandescent lamp bulb. The best results are secured when the reflecting coating is internally applied and the frosted area is located externally of the bulb. An approximate result is obtained when either the outside of the bulb is silvered and the inside frosted, or

when both the silvering and the frosting is done on the same side of the glass lamp bulb.

The perforations through the reflecting sur- 2 face, may be of any shape or pattern, provided only that in one dimension they be small. For example, a fine spiral line may be out over the entire reflecting surface by making a. simple adjustment on the rotating tool that is used to remove the silver from the transmitting portion of the bulb-since, on inside silvered bulbs the entire bulb surface is generally coated and the silver removed from the transmitting portion by scraping. By varying the 'rate of withdrawal of the scraping tool thespiral lines may be made close together or farther apart. They can all be of the same distance apart, or this distance may be varied, so as to permit more light to fall on the shadowed portion of the enclosure at the top, for example.

Approximately parallel lines-from the tip to the stemmay be made by withdrawing a tool having at its end a series of arms held outwards by springs, each with a suitable cutting or 0 abrading edge. If desired every other of these arms may be depressed, with suitable cams at approximately half stroke, so that in the neck portion the lines do not come too close together. By a suitable motion of the bulb while it is with- 5 drawn from this tool, approximately wavy lines may be out. A cross-hatched design may be made by superimposing these parallel lines on a spiral. Any suitable design may be employed, provided only that in one dimension the areas so removed are small. A chemical solution may be sprayed or injected into the silvered bulb, nitric acid or a solution of cyanide, for example, in the form of a very fine spray or mist, and each of the particles that settles on the silvered surface will -attack the silver and after washing with water minute perforations through the silver will permit some light to pass through the reflecting surface, and the desired result will be obtained. I do not desire to be limited to any exact pattern or to any precise process of producing the same; any

pattern and any distribution of fine cuts through the reflecting surface in connection with the frosted bulb surface will produce the desired effect.

It will be understood that my invention may be applied with advantage to lamps of gaseous discharge types or glow types, as well as those having filament light sources.

These and other features of the invention willbe best understood and appreciated from the following description of several preferred embodi ments thereof, selected forpurposes of illustration and shown in the accompanying drawings,

Fig. 1 is a view showing a lamp bulb in elevation within a sectioned globular enclosure.

Fig. 2 is a view in side elevation of a bulb associated with an external reflecting fixture.

Fig. 3 is a fragmentary sectional view on a 6 greatly enlarged scale of a portion of the bulb, and

Fig. 4 is a-view showing a bulb designed for indirect lighting within a conical enclosure which is shown insection. 10

In Fig. 3 is shown, on a greatly enlarged scale,

a section of the wall of a bulb embodying my invention in its preferred form. In this instance the glass 40 of the bulb is provided externally with a frosted or etched area 4|. This may be 15 produced by any suitable commercial process and its effect is to provide a surface made up of minute irregularities which have the property of diffusing light transmitted through or reflected by the surface in which they are formed. 'Upon its 2 inner surface the walls of the bulb are provided with a coating of a reflecting medium, such for example, as metallic silver. The reflecting coating 42, shown in Fig. 3, is removed in a pattern of flne spaced lines forming narrow apertures 43 25 through which light from the bulb may be freely transmitted. It will be understood that each ray of lightpassing through one of the apertures 48 is broken up and diffused by passing through the frosted surface 4|. Moreover, a considerable 30 portion is internally reflected by the frosted surface and then reflected outwardly again by the outer surface of the silver coating 42.

I have suggested in Fig. 3 the manner in which a single ray 44 of light is broken up and diflused 35 after passing in a normal direction through one of the apertures 43 and from this it will be seen that from each point of incidence with the frosted surface 4| a band or spot of diffuse light results.

It will be apparent that rays of light passing 40 through the apertures 43 at an angle to the sure face of the coating 42 will be subjected to even greater internal reflection and diffusion than the my 44 which has been shown in Fig. 3. In every case however some of the light is reflected back 45 to the outer surface of the silvered coating and eachof these back-reflected rays is again reflected toward the frosted surface. The twice reflected rays again strike the frosted surface and are in turn partly transmitted outwardly as dif- 50 fused light and partly reflected back to the silvered surface to be further reflected and diffused. The light which passes through the apertures 43 and is broken up and diffused in the manner suggested in Fig. 3 appears to cover a much wider area on the frosted surface of the bulb than the width of the aperture. For example, the brilliantly illuminated apertures 43 on a lighted bulb may appear to be at least 4; inch wide when actually the lines of the aperture 43 are 1/100 inch wide. 60 Besides this brilliant line of light the otherwise dark area behind the body of. the silvered coating is also rendered luminous. In other words, the light passing through the narrow apertures is fanned out so that the entire outer face of the o5 opaque reflecting coating appears luminous. Moreover, the light emanating from the area thus rendered luminous will be found to be polarized light. This is probably on account of the multiple -reflection to which the rays are subjected be- 7 tween the areas of inside reflecting coating and exteriorfrosted surface.

Theamount of light escaping through the flne apertures 43 is actually small. If the total area of'the apertures amounts to 5% of the silvered 75 area-much more than is necessary or used by me in the many embodiments of this invention that have been produced-the amount of light reflected by the coating 42 will not be reduced b more than 5% and the total light in the directed beam from the lamp will not be reduced by more than 3%.

Referring now to the installation illustrated in Fig. 1, the bulb I is provided internally with a silvered coating II which extends from the line of maximum bulb diameter upwardly into the neck of the bulb. This coating is removed in a number of fine circumferential lines l3 and these lines may be graduated in width or in location to control the amount of light which is to be allowed to escape through the otherwise opaque portion of the bulb. The outer surface of the bulb I0 is uniformly frosted in an area at least coextensive with the internal silvered coating. The curved end of the bulb l2 below the line of maximum diameter is clear and adapted to transmit a beam of high intensity comprising the light directly emitted by the filament of the bulb and the light reflected by its silvered coating II.

The bulb I0 is shown as being enclosed in a translucent globe I4 and by reason of the construction of the bulb the general effect of the globe to the observer will be that of uniform illumination. This is partly because the human eye is unable to make distinctions in illuminations of high intensity. While the eye can easily distinguish between 0.1 and 1.0 lumens per square foot it is unable to distinguish between 50 and 100 lumens per square foot. The iris of the eye automatically closes to a small opening in the presence of a bright light and this fact may account for the difference in perception under the circumstances discussed.

In Fig. 2 is shown a bulb 20 associated with an external reflecting fixture 24. The bulb 20 is frosted continuously over its entire area and provided with an external silvered coating 2| extending from the line of maximum bulb diameter upwardly into the neck of the bulb. The silvered coating is removed in a pattern of fine lines 23 formed as a continuous spiral. The dot and dash line 26 indicates the light pattern of the lamp when it is provided with a continuous silvered coating whereas the dotted line 25 indicates the actual light pattern of the lamp as illustrated. It will be noted that the intensity of downwardly directed light is very slightly reduced while an appreciable amount of light is transmitted upwardly through the apertures 23.

As viewed from one side of the lamp, it will be observed that by the spiral appearing in the silver coating there is presented a series of narrow spaced apertures.

A further embodiment of my invention is shown in Fig. 4 in which the bulb 30 is placed within a conical translucent enclosure 36 located apex downward. In this instance the bulb 30 is provided with an inside coating of silver 3| covering its curved end up to the line of maximum'bulb diameter. The entire exterior surface of the bulb is frosted. The silvered coating is removed in a series of meridian lines 33 which are supplemented by shorter parallel lines 34 in approaching the maximum diameter of the bulb. The silvered coating is also removed from the end of the bulb in a bulls eye 35. This pattern of silver removal results in an apparent uniform illumina tion of the enclosure 36 and it will be noted that all the silver has been removed from the end of the bulb which is directed toward the apex of the enclosure 36 and which is most remotely disposed with respect to the surface of the bulb.

I have referred to the removal of the silvered coating as being in a pattern of fine lines. The width of these lines may be in t e order of magnitude of the thickness of the {rib wall, particularly in the smaller sizes of lamps where the thickness of the glass is a small dimension.

The lamp construction of my invention has the great advantage that it affords a means for accurately controlling the photometric curve of light transmitted within the boundaries of the reflected area. If it is desired to cause a greater light flux to pass through one section of the reflecting area than through another section the reflecting coating may be removed in a pattern giving this result, 1. e., the lines of removal may be more closely arranged incertain sections than in others or they may vary in width.

Many modifications and changes in detail will readily occur to those skilled in the art without departing from the spirit and scope of my invention, but having set forth the objects and nature thereof and having shown and described illustrative examples of preferred embodiments, what I claim as new and desire to secure by Letters Patent is 1. An incandescent lamp having a bulb provided on a part of its inner surface with a reflecting coating and on its outer surface with a frosted area, the coating being apertured to present a series of narrow openings beneath the frosted area which render luminous the surface of the bulb outside said coating when the lamp is lighted.

2. An incandescent lamp having a bulb pro vided on a part of its inner surface with a reflecting coating and on its outer surface with a frosted area, the coating being apertured to present a series of long narrow adjacent openings beneath the frosted area which render luminous the surface of the bulb outside said coating when the lamp is lighted.

3. An incandescent lamp having a bulb with its outer surface roughened to diffuse transmitted light, and having an opaque metallic reflecting coating upon a portion of its inner surface, apertured in fine lines so located that the entire outer area of the opaque reflecting surface appears to be illuminated when the lamp is lighted.

4. An incandescent lamp having a bulb provided with an inner'metallic reflecting coating and a substantially coextensive frosted area, the

metallic coating being removed in a pattern of fine lines within the frosted area whereby the surface of the bulb outside the metallic, coating is rendered luminous when the lamp is lighted.

5. An incandescent lamp having a bulb provided with an inner metallic reflecting coating and a substantially coextensive frosted area, the metallic, coating being removed to provide a series of light-transmitting openings of a width approximating the thickness of the walls of the bulb and spaced from each other so that the intermediate areas in the .outer surface of the coated portion of the bulb appear to be luminous when the lamp is lighted.

6. An incandescent lamp having the bulb provided with a reflecting coating and a superposed external frosted surface, the reflecting coating being removed in a comprehensive pattern of fine lines so arranged that the light flux escaping through the lines of the reflecting area is not more than of the light reflected by the reflecting coating.

7. An incandescent lamp having a bulb provided'on a part of its inner surface with a reficting coating having a spiral light-transmitting line therein and on its outer surface being pro- 5 vided with a frosted area superposed in part above the reflecting coating. 

